The present invention relates to a filtering technique for high frequency signals, and more particularly to a technique that can be effectively applied to the removal of harmonic contents propagating over the surface of a semiconductor chip or elsewhere.
In recent years, cellular phones have come into extensive use as one major means of mobile communication, and their functions are required to be even more diverse. For instance, the requirement for size reduction of high frequency power amplifier modules for cellular phones is particularly stringent, and to meet this requirement such modules which accommodate on a single chip communication formulas for different frequency bands, such as GSM and DCS, are extensively used.
Where communication formulas for different frequency bands are accommodated on a single chip, high frequency contents supplied from one frequency band affects the other frequency band and thereby seriously deteriorates the so-called cross-band isolation level.
For this reason, a filtering circuit consisting of a PIN diode and a capacitor is provided in the output matching circuit on the side where high frequency contents leak out in the high frequency power amplifier module to cope with this problem by filtering high frequency contents when one frequency band is put to work.
Incidentally, some such high frequency power amplifiers have in their output matching circuits a plurality of output side micro-split lines for delivering different signals, and prevent interference between one output side micro-split line and the other output side micro-split line by providing a plurality of GND lines between the output side micro-split lines (see Patent Reference 1 for instance).
Patent Reference 1: Japanese Unexamined Patent Publication No. 2002-141756